Then I strongly suspect there is some discrepancy on one of the nodes you've set up.  I could imagine moire or some other kind of artifact, but a simple color difference that is that blatant is pretty unlikely to be the mesh's fault - particularly in your preview before it is even applied to a mesh, it's on a flat surface that is previewed exactly the same way for any surface regardless of polygon shape, size or count (I'm pretty sure anyhow).  Try saving your duplicated material and applying it to a cube or something and see if the color difference is still there.

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